Question

Using regex in C# I should replace one word if it doesn’t have specific one before
In my example it to replace “Ballmer” with “Steve Ballmer”

In:

...text...Ballmer...text

Result:

...text...Steve Ballmer...text

but if “Steve” already there, I shouldn’t add Steve again.

In:

...text...Steve Ballmer...text

Result:

...text...Steve Ballmer...text

Thanks.

Answer 1

Use negative lookbehind (?<!...) and positive lookahead (?=...)

string output = Regex.Replace(input, @"(?<!Steve )(?=Ballmer)", "Steve ");